At present, generally two kinds of weft inserting methods and apparatus in jet looms are known. In accordance with the first such method and apparatus, the weft yarn is inserted into the shed by a single fluid jet. However, this is disadvantageous for the insertion of weft threads over large weaving widths, since the fluid velocity, by which the weft thread is being inserted into the shed, is reduced as it flows freely into the shed space approximately exponentially in dependence upon the distance from the orifice of the inserting nozzle. The use of a confusor, that is, a jet guiding means, improves weft insertion since along the guiding means the velocity of the fluid jet is reduced in upon the distance from the nozzle orifice approximately linearly. In spite of this, weaving widths up to two meters remain a classical limit to weft insertion by means of a single fluid jet.
The second manner of weft insertion employs, beside the inserting fluid jet, secondary, weft entraining fluid jets which, either simultaneously, or successively, aid in the insertion of the weft yarn into the shed. A plurality of successive weft insertion means such as nozzles situated within the shed of the loom are known; by means of such secondary nozzles, the insertion of the weft yarn throughout the whole weaving width is assured.
The secondary nozzles are arranged e.g. on a beam in either the upper or lower part of the shed. In the course of weft yarn insertion, fluid flows from the secondary nozzle orifices, such fluid entraining weft and causing it to be fed through the shed. An assembly of secondary or auxiliary nozzles is used, arranged near one another in a varying geometrical arrangement. The secondary nozzles can be either firmly connected to the reed of the loom, or driven by means of a mechanism which controls their penetration into the shed. An arrangement of secondary nozzles in the form of a asymmetrical saw-shaped bar is also known, which is pressed into the open shed against the warp threads. In the shorter walls of the saw-shaped bar, which are approximately vertical, drain openings of the nozzles are arranged, the direction of the drain openings being approximately in the direction of weft insertion. The nozzle thus arranged can be situated at the lower side or on both sides of the weaving shed.
However, the above-described known methods and apparatus have not proved to be entirely satisfactory from the viewpoint of weft yarn insertion. In reliable weft yarn insertion, the weft yarn must be fed in it insertion throughout the entire weaving width without loops, breakages and short picks. When eliminating loops in the weft caused by the warp, by trapping them in an uneven shed, then the motion of the weft thread, particularly that of its front end, is decisive from the view point of the proper insertion of the weft yarn. The weft yarn should move, if possible, without oscillations to reduce the possibility of its being trapped in the warp threads, to prevent its escape from the shed, etc.
In the insertion of weft yarn by means of a primary, inserting fluid jet and secondary, entraining fluid jets hitherto known, the tip of the weft yarn to be inserted is deflected from the direction of weft insertion. The geometrical arrangement of the secondary, entraining nozzle is, therefore, in addition to its primary action, i.e. the supporting of the weft insertion, simultaneously directed to a determination of a narrow weft passage space. There are known prior methods in which half of the weft yarn passage is determined by a plurality of plate-like guide members of various cross section, which are connected to the reed either fixedly, or movably. Upon weft insertion, such plate-like guide members are disposed in the shed and perform, together with the entraining nozzles, the directing of the weft yarn carrying fluid jet. The spacing between successive plate-like guide members varies from 10.sup.-1 to 10.sup.-4 m, and their shape varies from an open one up to a closed cross section with an unthreading groove for the weft yarn. The entraining nozzles either form part of the plate-like guiding members, or are made separate from them.
It is also known that weft yarn insertion into a shed wherein the planes of the shed-forming threads are covered, both from above and from below by plates which are deflected upon beat-up. By covering the shed, an air channel is formed. This arrangement can be integrated with plate-like guide members and nozzles. For the purpose of stabilizing the weft yarn, air is sometimes sucked off from between the plates.
The above-described known arrangement are intended for stabilizing the position of the weft yarn by an aerodynamic action of the air jet in the center of the shed or in its proximity in such manner that no contact of the weft thread takes place either with the upper or the lower shed, as well as with the reed.
In another known arrangement, the plate-like guiding members are integrated into the reed in the form of shaped reed dents. In this arrangement, it is intended that the weft yarn be guided between two nose-shaped projections of the shaped reed dents.
Only some of the above-described known weft yarn inserting arrangements are in practical use because the others have either one or more practical disadvantages. Weft insertion through a confusor, that is, a plurality of plate-like guide members, constitutes no more than half of the weft inserting arrangement in use, since the confusor, upon penetrating the shed, scuffs and/or fibrillates the warp threads and damages them in various other manners. An acceptable reliability is achieved only with shorter insertion lengths. By using an entraining fluid jet system, however, one of the main advantages, low air consumption, of the confusor is lost.
The known inventions, which aim at maintaining the weft yarn in proximity to the shed by means of directing nozzles are disadvantageous because weft insertion takes place far from the first heddle, supporting shaft at such points, which might bring about a considerable risk of an uneven shed and of insertion failure resulting therefrom. The directing of nozzles and the stabilization of pressure in front thereof must be exactly defined. The application of guiding gliders, together with an increasing density, to a profile reed, which might be preferable, is secured mechanically. This is done by defining the path; however, this arrangement is extremely susceptible to changes in the adjustment of the direction of the outflow of the fluid and its pressure inside the nozzles. The profile reeds are expensive, vulnerable to wear and impairment, and must be frequently exchanged when changing the nature of goods being woven. The formation of a channel from plate-like members within the proximity of the shed, its interconnection with both the gliders and nozzles is clumsy, makes for increase attendance, and requires and additive mechanism.
The present invention has among its objects the removal to an extend hitherto unknown of the disadvantages of the prior art, without using a guiding channel, whether formed by a system of gliders, a profile reed, or a plurality of plate-like guide members.